why s120 controlled bridle motor shake after even stop command

hi

i have a small problem in my running galvanizing line.

i have AC induction motors. some times when operator want to stop the bridle then bridle master motor shake in stand still position.

it is controlled by s120  double motor module drive.For one motor mode of control is speed control with encoder and for other one is speed control encoderless.

its basically working on bridle in galvanizing line so its a master and slave principle.

Master has encoder feedback and slave has reference from master about speed. 

so i don't under stand why some time it stop normally and some time it shakes in stand still position.

hello team,

Thanks for the reply 

let me clarify more about bridle. in galvanizing line bridle is the one which pulls the MS sheet from one section to another so sheet thickness is not going to change during start and stop.bridles are the one who  maintains tension  in sections.

i have a problem in exit section where we have recoiler and bridle. bridle moves sheet and gives to recoiler (Recoiler is coiling the galvanize sheet).

so when operator press stop button then recoiler and bridle both have to stop but some time bridle master motor stops normally but start shaking on zero speed there is no fault in drive s120.

 In other case some time recoiler and bridle both stops and there is no shake.

Now i am thinking that is there any problem with bridle breaking coz we have external pneumatic control brakes on bridle motors or when recoiler  ramp up time is short then bridle ramp up time difference is 1 second.

when ever bridle start shake then there is no present fault in s120 so we switch off BLM then switch on again bridle stop shaking then we start line its running normally.